Water sports are popular, particularly for recreation and as a form of exercise. Few types of watercraft, however, use human power (i.e., work or energy produced from the muscles of the human body). Rowing or paddled watercraft; such as boats, canoes, kayaks, and the like; have traditionally served users wanting to experience the water while getting physical exercise. However, disadvantages exist with paddled or rowing watercraft. Rowing or paddling tends to be quite inefficient as a propulsion method. Moreover, friction or drag associated with the interaction of the watercraft and the water limits achievable speeds.
Reducing the resistance of water against forward motion increases the efficiencies and speeds achievable by watercraft. Hydrofoils reduce this resistance when employed in motor-powered watercraft. Such watercraft use hydrofoils to achieve lift, often raising the watercraft hull completely out of the water. This lifting reduces drag on the watercraft by reducing water resistance.
In nature, applying force to a hydrofoil in a direction generally perpendicular to the water stream is a method of propulsion used by many swimmers. Dolphin, orcas, bluefin tuna, and the like achieve great speeds by applying near perpendicular force to their tails, which act as hydrofoils.
Many human exercise machines employ, among other things, resistance of a user's weight against gravity to produce a desired exercise workout. Examples of popular exercise equipment include stationary bikes, treadmills, stair steppers, and elliptical bikes. However, many of the user-friendly aspects of such equipment are not present in personal, human-powered watercraft, making such watercraft less desirable for exercise use.